1. Field of the Invention
The present invention relates to a carrier for a double side polishing apparatus and a double side polishing apparatus using the same, and more particularly, to a carrier on which a wafer's physical location can be adjusted to induce an optimum quality polishing process, and a double side polishing apparatus using the same.
2. Description of the Related Art
Mainly, a silicon wafer fabrication process includes a slicing process for slicing a single crystal ingot into thin disc-shaped wafers, a chamfering process for chamfering the edges of the wafer to prevent defects of the wafer such as crack, chipping, fissure and so on, a lapping process for flattening the wafer, an etching process for removing any residual damage from the wafer, a polishing process for mirror-polishing the surface of the wafer, and a cleaning process for removing impurities from the wafer. Additional processes may be added or a fabrication process sequence may be changed according to fabrication environment, specification of a target wafer and so on.
The polishing process may be classified into a single side polishing process and a double side polishing process. The double side polishing (DSP) process polishes both sides of a wafer, i.e., an upper side and a lower side.
A double side polishing apparatus used to perform the double side polishing process is described below in detail with reference to FIG. 1.
The double side polishing apparatus 10 comprises an upper polishing plate 150 having a polishing pad attached to a lower surface thereof, a lower polishing plate 110 installed opposite to the upper polishing plate 150 and having a polishing pad attached to an upper surface thereof, and a carrier 130 installed between the upper polishing plate 150 and the lower polishing plate 110 for mounting a wafer 100 to be polished.
An internal gear 120 is located along the outer periphery of the lower polishing plate 110, and a sun gear 140 is installed at the center of the double side polishing apparatus 10. At least one carrier 130 having a wafer mounted therein is engaged with the internal gear 120 and the sun gear 140, and rotates accordingly.
As the carrier 130 rotates by the internal gear 120 and the sun gear 140, a wafer mounted in the carrier 130 also rotates. A frictional force is generated by a rotational motion between the wafer and the polishing pads of the upper and lower polishing plates 150 and 110 in contact with the wafer. The wafer is polished by the frictional force together with a reaction of a polishing slurry containing abrasive particles and various kinds of additives.
The internal gear 120 and the sun gear 140 are capable of independent rotation. The extent (cycle, number of times and so on) of revolution and rotation of the carrier is determined according to a rotational speed of each gear 120 and 140 about an axis.
The wafer mounted in the carrier 130 makes a rotational motion corresponding to the extent of revolution or rotation of the carrier 130.
Meanwhile, the upper and lower polishing plates 150 and 110 of the double side polishing apparatus 10 are manufactured through a lapping process. Thus, although the upper and lower polishing plates 150 and 110 are manufactured by the same manufacturer, they may have a processing deviation caused by the lapping process in consideration of size (of the upper polishing plate or the lower polishing plate), and may have different flatness or shapes for each manufacturer as shown in FIG. 2.
As shown in FIG. 3, repetition of the polishing process at a great pressure increases the temperature of the upper and lower polishing plates, resulting in physical deformation of the upper and lower polishing plates. In FIG. 3, a dotted line shows a temperature change of a base of the lower polishing plate, and a solid line shows a surface temperature change of the upper and lower polishing plates.
In consideration of the fact that the polishing process proceeds for a considerable time and at a considerable number of times, the physical deformation may be understood as a time-varying phenomenon. Thus, various factors such as the state of a slurry, dressing conditions and so on may be dynamic factors that are impossible to be determined quantitatively.
Under this circumstance, if wafer flatness and so on does not meet the standard quality, conventionally a carrier or a polishing plate was replaced by new one. However, the conventional technique is based on component replacement, and this replacement operation often requires a quality test for flatness and so on, resulting in prolonged process time. And, because a carrier and a polishing plate are replaced at an early stage, there is a considerable economic damage of raw subsidiary materials.
The conventional polishing apparatus has a wafer mounting hole of a fixed location, and thus repeatedly forms uniform rotation traces. For this reason, when flatness of a polishing plate or other dynamic factors vary, the conventional polishing apparatus can not take active measures against the varying environment. This is a fundamental problem of the conventional polishing apparatus.
Meanwhile, a carrier performs the most important function among flatness control factors in a double side polishing process. Generally, the carrier is made of epoxy glass or SUS DLC. Here, the SUS DLC is stainless steel with carbon coating.
Referring to FIG. 4, a carrier 130 having a wafer 100 mounted therein is interposed between an upper polishing plate 150 having an upper pad 151 attached thereto and a lower polishing plate 110 having a lower pad 111 attached thereto. The carrier 130 has a gear part along the outer periphery thereof. The gear part is engaged with an internal gear 120 at the inner periphery of a polishing apparatus and with a sun gear 140 at the outer periphery of the polishing apparatus.
The rotational momentum or torque by revolution and rotation of the carrier, in particular, an epoxy glass-made carrier is greatly applied to the outer periphery of the carrier having the gear part engaged with the internal gear and the sun gear. As the rotational motion continues, the applied force continues to accumulate at the outer periphery of the carrier, and in the end, cracks occur to the outer periphery of the carrier as shown in section A of FIG. 5.
The crack causes damage to an edge area of a polishing pad facing a wafer, and consequently, the pad is deformed and has an uneven surface. As a result, there is a deterioration in flatness of the wafer to be polished. And, substances detached from the damaged pad are included in the slurry, thereby making it difficult to filter the slurry.
That is, the epoxy-made carrier has risks of early deterioration in pad conditions caused by damage to the outer periphery thereof and reduction in flatness at wafer polishing. Further, the life cycle of the carrier is decreased.
Meanwhile, an SUS DLC-made carrier has higher rigidity than the epoxy-made carrier, and thus, has relatively less damage to the outer periphery thereof. However, the SUS DLC-made carrier has a limitation in thickness control, consequently a limitation in ensuring flatness of stable quality.